There are several types of sights available in the market to enable a user of a weapon such as rifle, shotgun, handgun, and submachine gun to aim these weapons. Examples of such sighting devises include laser sights, holographic sights, and “reflex” or “red dot” sights. Holographic sights utilize a holographic optical element (HOE), illuminated by a reconstruction beam, and the HOE reconstructs an image, typically of a reticle. A user looks through the HOE at a targeted object and perceives the reconstructed reticle.
FIG. 1 schematically illustrates an example of such a prior art device. A light source 2, typically a laser diode, projects a diverging beam of light 3 that is reflected by a mirror 4 or HOE, such as a grating, creating a reflected beam 5. The reflected beam 5 in this example is also diverging, and may be considered a reconstruction beam. Alternatively, the beam may be collimated. The reconstruction beam 5 illuminates a holographic optical element (HOE) 6 and the HOE 6 reconstructs an image of a reticle. An individual's eye 7 can view the image of the reticle and a target (not shown) through the HOE 6. These reticles may be illuminated for use on low-light or daytime conditions. With any illuminated low-light reticle, it is generally desirable that its brightness can be adjusted. A reticle that is too bright may cause glare in the user's eye, interfering with his ability to see in low-light conditions. This may be because the pupil of the human eye closes quickly upon receiving any source of light.
FIG. 2 schematically illustrates an example of a prior art device with a configuration that uses collimated light. A light source 10, typically a laser diode, projects a diverging beam of light 11, which passes through a collimating lens 12. This creates a collimated beam of light 13. The collimated beam 13 illuminates a diffraction grating 14. The diffraction grating 14 produces a reconstruction beam 15 that is angled upwardly, in this example, which illuminates an HOE 16. The HOE reconstructs an object beam 17 that is perceived by a user's eye 18. The object beam 17 is angled downwardly, in this example, such that the object beam 17 and the collimated beam 13 are parallel to each other. The grating 14 and HOE 16 are also parallel to each other.